This investigation of behavioral and hormonal responses to common laboratory experiences in macaques has found individual differences in various measures of psychological well-being. We collected additional data to characterize the individual differences using measures found by others to have trait-like qualities of relevance to personality. We collaborated with Dr. Randall Kyes to investigate aggressive-reactive personality traits and brain serotonergic responsivity. The longtailed macaque subjects of our previous studies were tested in Dr. Kyes' Standardized Behavioral Assessment Procedure. The assessment apparatus consisted of a panel with a rear projection screen window that can be pushed up to within 30 cm of a single cage. A set of seven visual stimuli (photographic slides) depicting a range of stimulus contents including a laboratory technician with leather capture gloves, a threatening monkey, two monkeys grooming, inanimate objects, blank image, etc., were pre sented to each subject. The animal's responses were recorded via closed-circuit television from a camera mounted below the projection screen and are being scored. Several days after testing, cervical spinal fluid was sampled and will be assayed for 5-HIAA, HVA, and other substances. Brain serotonergic levels, behavioral reactivity to slides, cardiac reactivity to a potential stressor (laboratory technician with leather capture gloves), rating scales of personality, urinary cortisol responses to stressful vs. non-stressful laboratory experiences, and various behavioral measures scored from videotapes during previous studies of these subjects are being analyzed to identify personality types. The goal is to enhance the understanding of nonhuman primate psychological well-being, and the factors promoting it. It is important to identify those features of the laboratory environment that affect research macaques independent of personality type, and those features that primarily affect only the most reactive monkeys. Supported by NIH Grants RR00166 and RR04515. Bowers, C.L., Crockett, C.M., and Bowden, D.M. Differences in stress reactivity of laboratory macaques measured by heart period and respiratory sinus arrhythmia. Am. J. Primatol. 45:245-261, 1998. Crockett, C.M. Psychological well-being of captive nonhuman primates Lessons from laboratory studies. Pages 129-152 in Environmental Enrichment for Captive Animals, edited by D. Shepherdson, J. Mellen, M. Hutchins. Washington, D.C. Smithsonian Institution Press, 1998. Crockett, C.M., Bellanca, R.U., Bowers, C.L., and Bowden, D.M. Cortisol responses of longtailed macaques to increased social stimulation. Am. J. Primatol. 45:175, 1998 (abstract).